Bioenergetics… sounds fancy right? That’s because it is! It is a system that few besides the formally educated even know exist. To follow is a snapshot of the first few weeks of my exercise science degree – this article will summarize very complex and absolutely necessary processes of the body covered in college-level exercise physiology and sports nutrition courses.
What Makes Your Body Move?
To begin, what makes your body move? You have a skeleton, and these bones are moved by the muscles attached to them. Myosin is a tiny part of the muscle that pulls on another part called actin to contract the muscle, but what makes all of this happen? ATP, or adenosine triphosphate, is put into action with every tiny movement that your body makes. When you blink your eye, ATP. When you pick up a fork, ATP. When you push as hard as possible to get up under the squat bar, ATP. Your body absolutely requires and depends on the availability of ATP to perform any action.
With that being said, it would make sense that our body has a rather impressively-sized reservoir of ATP, correct? Well, it does not. The amount of ATP your body keeps on hand is positively minuscule; in fact, it allows for no more than just a few seconds of movement before depletion. How can this be so? Because the human body is incredible at synthesizing ATP rapidly. There are three ways that the body can create more ATP, and that is what bioenergetics details.
It is important to note that all three systems are utilized at all times, though we primarily rely on one for the given activity being performed. The first energy system is the phosphagen system. This is the fastest ATP generating process and enables us to move with maximum power. Your muscles use creatine to replenish ATP stores as you work at full capacity. The only issue is that this cannot be sustained for longer than 8 to 10 seconds.
Now, as I’m sure you’re wondering, is this the same creatine that you put in your shakes is what is being referenced here? This is the reason people take creatine; it saturates the muscles and fuels the phosphagen system for just a little bit longer. That means more power, and for just a little bit longer. That’s why you can get those extra few reps! This is also the reason that taking creatine will not help you perform better while going for a run. The phosphagen system is most active when you are lifting weights within the 1 to 5 rep range, or sprinting away from a bear for example.
In Come Carbs…
Moving from the immediate energy system, we now have a relatively fast energy system to cover. The glycolitic pathway is what puts all of those carbs to use! This process takes glycogen, which is an accumulation of glucose, and turns it into ATP. Glycogen has to go through quite a few reactions in order to produce ATP; therefore, it takes more time. Glycolysis can sustain activity that is quite intense for up to two minutes at a time. The process of turning glycogen and glucose does not require oxygen, nor does the phosphagen system, making both of these anaerobic systems (meaning they do not need oxygen).
Byproducts from the glycogen system do require oxygen however. Ever hear of lactic acid? It’s responsible for the burn you feel from a 15 rep set of cable tricep extensions to failure. Oxygen is used to clear metabolites in the muscle to prevent this lactic acid build up from glycolysis. When the build up grows and need for oxygen outweighs supply, lactic acid forms and interrupts the muscle’s movements. The glycolytic pathway is used predominantly when effort is high and not sustainable for long, such as a set of 12 squats or swimming a few laps in the pool.
Lastly, the slowest, yet most powerful system in our body is aerobic respiration. Oxygen from the lungs comes to allow the full breakdown of carbohydrates. Carbs can be utilized from remaining stores in the muscle or from the liver and intestines. Fatty acids can also be used, called beta oxidation, your body strips the adipose tissue and burns it for fuel. On average, a person has 100,000 calories in reserve via adipose tissue. Think of that the next time you’re hungry!
The human body will also burn proteins for fuel, but this largely only occurs in extreme conditions and starvation. When aerobic respiration kicks in, the body can continue to move for an essentially unlimited amount of time at a certain work capacity as long as there is fuel (carbs, fats, protein.)
To wrap this up in an easy-to-digest message, let’s summarize by playing out a scenario. You are standing in line at a coffee shop, and the man behind you takes your wallet and runs out the door. You turn and sprint after him. During the first three seconds, you will use the ATP in reserve and begin to very quickly create more ATP. You run down the street after the man that has a head start on you and start to feel yourself slowing down, though you are still determined to catch up and run as fast as possible.
At this time, about 10 seconds after the theft, you have just about run out of creatine in the muscle and can no longer support an all-out sprint. You begin to use carbohydrates with the 12 step process of glycolysis; this fuels your fast paced run for the next two minutes. As you wonder why no one else has stopped this guy, he runs down alleys, across streets, and out to a field. You realize if you are going to catch him you’ll have to pace yourself.
You slow down a little and plan for the long haul. Now, you’re using aerobic respiration, breathing and moving at a rate that can support your continued effort. Eventually you catch the guy; good thing you knew what was going on in your body! Oh, and you get the girl too!